The Similarities of Optokinetic After-Nystagmus to the Vestibular Nystagmus

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Abstract
Optokinetic after-nystagmus (OKAN) was investigated quantitatively in the rhesus monkey to clarify the physiological characteristics. OKAN was always induced after optokinetic nystagmus (OKN) in darkness, was dependent on the preceding OKN and increased up to 135°/sec. OKAN was not influenced by changing the period of OKN. OKAN was very strongly suppressed in light, but the responses were still dependent on the preceding OKN. The responses of OKAN were not changed by the level of illumination during OKN. OKAN showed the response decline in the repetitive testings on one day and in daily tests in all parameters of OKAN. Also, OKAN had a secondary phase. Thus there were many similarities between OKAN and the vestibular nystagmus induced by caloric or rotatory stimulation.